Sodium hydroxide (also referred to as caustic soda or lye; NaOH) is a white, hygroscopic solid. Due to its negative enthalpy of solution of -44.4 kJ / mole, it dissolves very well in water to the strongly alkaline sodium hydroxide solution. A lot of heat is released in this process. It reacts with the carbon dioxide in the air to form sodium hydrogen carbonate and is therefore stored in hermetically sealed containers. It can be stored together with a desiccant to prevent caustic soda from binding water from the air. A hydroxide ion as a strong base displaces weaker and volatile bases from its salts.